This statement shows that Anne looks for the good in people and tries to be optimistic about the world.
Despite everything terrible that is happening around them, Anne still believes that people are basically good. This is a remarkable statement to make. Anne is hiding from the Nazis, and she constantly hears about suffering and death. Yet, she is still able to have a positive viewpoint on human nature.
ANNE. We're not the only people that've had to suffer. There've always been people that've had to ... sometimes one race ... sometimes another ... and yet ...
PETER. That doesn't make me feel any better! (Act 2, Scene 4)
Anne tells Peter that she feels like the world goes through phases, just like people do. As a young adult, Anne has experienced many phases for herself. She seems to think that the world needs to grow up.
In essence, Anne feels that she can find good in the world by taking comfort in the good things that people do. She feels that for all of the bad she has seen, she has seen a lot of good.
When I think of all that's out there ... the trees ... and flowers ... and seagulls ... when I think of the dearness of you, Peter ... and the goodness of the people we know ... Mr. Kraler, Miep, Dirk, the vegetable man, all risking their lives for us every day ... (Act 2, Scene 4)
Peter’s perspective is that they did not get their chance, like their parents did. They did not really get to live. He is more pessimistic. He does not believe things will end well, and is not so quick to see the good in people.
Anne died young, but the perspective that she wrote about in her diary has served as an inspiration for many people since. In the bleakest of circumstances, Anne could believe that people are good at heart. If she could, maybe we can.